1. Field of the Invention
The present invention relates to a portable apparatus and a portable timepiece provided with a push button.
2. Description of the Related Art
Among portable timepieces such as a wrist watch or a pocket watch or portable apparatuses such as a stop watch, a mobile phone or a personal digital assistant, there has been known a portable timepiece or a portable apparatus where a push button which operates a contact or the like in the inside of an apparatus exterior body is mounted on the apparatus exterior body. By pushing the push button with a predetermined stroke, for example, in the portable timepiece, a dial can be illuminated, or a time display can be changed from an analogue display to a digital display or from a digital display to an analogue display, or date and day which are digitally displayed can be corrected.
This type of portable apparatus is configured such that the push button is biased in the direction opposite to the pushing direction of the push button by a spring and hence, the removal of the push button from a pipe to the outside is prevented by a force of the spring. As such a removal preventive constitution, on an end portion of the push button which reaches the inside of an apparatus exterior body through a pipe fixed to the apparatus exterior body, a C-type or an E-type retainer ring which is engaged with an end of the pipe is mounted.
On the premise of such a constitution, a conventional portable apparatus includes a locking member which prevents an erroneous operation of the push button. The locking member has a female threaded portion formed on the inner periphery thereof threadedly engaged with a male threaded portion formed on the outer periphery of the pipe fixed to the apparatus exterior body, and the locking member is movable between a locked position and an unlocked position by a change in meshing engagement of these threaded portions (see JP-A-2003-7164 (patent literature 1), for example).
In such a constitution, when the locking member is moved to the unlocked position, the locking member is moved away from a head of the push button which passes through the pipe. Accordingly, a pushing operation of the push button is allowed with a stroke corresponding to a distance by which the locking member is moved away from the head. To the contrary, when the locking member is moved to the locked position, the locking member is brought into a state where the locking member is in contact with the head of the push button. Due to such a constitution, forced pushing of the push button can be prevented.
Further, there has been also known a prior art where the external appearance of the push button does not change between a locked state and an unlocked state and, further, the intrusion of debris into the female and male threaded portions is made difficult even in a locked state (see JP-A-2004-319446 (patent literature 2), for example).
In such prior art, the locking member is axially movably fitted on the outer periphery of the pipe fixed to the apparatus exterior body, and a rotary ring which covers the locking member is held such that the rotary ring is not axially movable with respect to the pipe. A female threaded portion formed on the inner periphery of the rotary ring is threadedly engaged with the male threaded portion formed on the outer periphery of the locking member. Due to such a constitution, the locking member can be moved between a locked position and an unlocked position by changing meshing engagement of these threaded portions.
In such a constitution, when the locking member is moved to an unlocked position along with the rotational operation of the rotary ring, the locking member is moved away from the head of the push button which passes through the pipe. Accordingly, the pushing operation of the push button is allowed with a stroke corresponding to the spaced-apart distance between the locking member and the head. To the contrary, when the locking member is moved to a locked position due to the rotation of the rotary ring, the locking member is brought into a state where the locking member is in contact with the head of the push button. Accordingly, the forced pushing of the push button is prevented.
In the prior art, the push button is positioned due to the engagement of the retainer ring mounted on the push button with the end of the pipe in the inside of the apparatus exterior body, and the locking member moved to the locked position is brought into contact with the head of the push button in such a state. Due to such a constitution, even in a state where the push button is locked, a state where the male threaded portion and the female threaded portion are engage with each other is maintained.
There may be a case where, after the locking member reaches the locked position, the locking member having the female threaded portion or the rotary ring is further rotatably operated excessively due to an operator's error.
Such an erroneous operation may occur due to the following reason. That is, the strength of the retainer ring is not so large, and the retainer ring is elastically deformable relatively easily. Further, the retainer ring has a slit so that the retainer ring is deformable in order to shrink a diameter thereof. Accordingly, it is scarcely possible for a user to perceive that the locking member has reached the locked position due to the elastic deformation of the retainer ring. Accordingly, the locking member or the rotary ring may be in error operated as described previously.
When the locking member or the rotary ring is rotatably operated excessively in error, there may be a case where the deformed retainer ring is pulled into the inside of the pipe along with such a rotary operation. As a result, there may be a case where the smooth movement of the push button in the axial direction is impaired after the erroneous operation. Particularly, when the locking member or the rotary ring is designed so as to have a larger outer diameter for enhancing the operability of the locking member or the rotary member, a rotational torque caused by the above-mentioned erroneous operation is increased. Along with the increase of the rotational torque, the retainer ring is more easily deformed thus increasing a possibility that the retainer ring will be pulled into the inside of the pipe. Further, the drawbacks brought about by the above-mentioned erroneous operation become a cause of impairment in designing the locking member or the rotary ring with a larger outer diameter.
As a countermeasure to cope with the above-mentioned drawbacks, it may be considered that a wall thickness of a retainer ring is increased or a retainer ring is made of a material having high strength so as to make the deformation of the retainer ring difficult. However, such a countermeasure uses a dedicated retainer ring which is yet to be developed and hence, a manufacturing cost is pushed up. In addition, an operation of mounting a retainer ring on a shaft portion of a push button or an operation of removing the retainer ring from the shaft portion of the push button becomes cumbersome so that operability is largely lowered when a push button and parts around the push buttons are disassembled and cleaned. Accordingly, the above-mentioned countermeasures are not desirable.